192 MORPHOLOGY AND EVOLUTION (fig. 35, A), there are three palmar interossei adducting the fingers towards the medius. In the latter there are six palmar interossei: three—those to the ulnar side of the index and the radial sides of the annularis and minimus—are similar to the palmar interossei of the other Primates ; the other three—to the sides of the medius and ulnar side of the annularis—are really dorsal interossei which act as abductors. MUSCLES OF THE LEG. The psoas parvus arises from the last dorsal and upper one or two lumbar vertebrae in the large Simiidse; but it rises from the first three in the Gibbon. It is inserted into the ilio-pectineal line; the insertion is farthest forwards in the Chimpanzee in which it is attached close to the femoral vessels. The iliacus arises as in Man. It is fused with the quadratus lumborum in the Chimpanzee. The psoas magnus varies considerably as regards its origin. In the Chimpanzee it blends more with the iliacus than in Man. It arises from the last dorsal vertebra, the inner inch of the last rib and the transverse processes and centra of the four lumbar vertebrae. It is inserted as the ilio-psoas into the lesser trochanter and the femoral shaft a little below it. In the Gorilla it arises from the bodies of the first three lumbar vertebrae and intervertebral discs, the third lumbar transverse process and the crista ilii. In the Orang it springs from the last dorsal and all lumbar vertebrae, and in the Gibbon it also arises from the tendon of the rectus femoris.